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MIKE 2017
MIKE 21
Hydrodynamic Module
Step-by-step training guide
mike21_hd_step_by_step.docx/NHP/2016-07-07 - © DHI
DHI headquarters
Agern Allé 5
DK-2970 Hørsholm
Denmark
+45 4516 9200 Telephone
+45 4516 9333 Support
+45 4516 9292 Telefax
www.mikepoweredbydhi.com
i
CONTENTS
MIKE 21 Hydrodynamic Module Step-by-step training guide
1 Introduction ....................................................................................................................... 1 1.1 Background .......................................................................................................................................... 1 1.2 Objective of Training Example ............................................................................................................. 2 1.3 Tasks to be completed to form a Complete Hydrodynamic Setup ...................................................... 2
2 Creating the Bathymetry .................................................................................................. 3
3 Creating the Input Parameters ....................................................................................... 11 3.1 Generate Water Level Boundary Conditions ..................................................................................... 11 3.1.1 Importing measured water levels to time series file ........................................................................... 12 3.1.2 Creating boundary conditions ............................................................................................................ 17 3.2 Initial Surface Level ............................................................................................................................ 19 3.3 Wind Conditions ................................................................................................................................. 19 3.4 Density Variation at the Boundary ..................................................................................................... 21
4 Model Setup .................................................................................................................... 23 4.1 Flow Model ......................................................................................................................................... 23 4.2 Model Calibration ............................................................................................................................... 33 4.2.1 Measured water levels ....................................................................................................................... 33 4.2.2 Measured current velocity .................................................................................................................. 34 4.2.3 Model extraction ................................................................................................................................. 36 4.2.4 Compare model results and measured values .................................................................................. 40
MIKE 21
ii Hydrodynamic Module - © DHI
Introduction
1
1 Introduction
This training example relates to the fixed link across the Sound (Øresund) between
Denmark and Sweden.
Figure 1.1 The Sound (Øresund), Denmark
1.1 Background
In 1994 the construction of a fixed link between Copenhagen (Denmark) and Malmö
(Sweden) as a combined tunnel, bridge and reclamation project commenced. Severe
environmental constraints were enforced to ensure that the environment of the Baltic Sea
remains unaffected by the link. These constraints implied that the blocking of the
uncompensated design of the link should be down to 0.5 %, and similarly, maximum
spillage and dredging volumes had been enforced. To meet the environmental constraints
and to monitor the construction work, a major monitoring programme was set up. The
monitoring programme included more than 40 hydrographic stations collecting water level,
salinity, temperature and current data. In addition, intensive field campaigns were
conducted to supplement the fixed stations with ship-based ADCP measurements and
CTD profiles. The baseline-monitoring programme was launched in 1992 and continued
into this century.
By virtue of the natural hydrographic variability in Øresund, the blocking of the link can
only be assessed by means of a numerical model. Furthermore, the hydrography of
Øresund calls for a three-dimensional model. Hence, DHI's three-dimensional model,
MIKE 3, was set up for the entire Øresund in a nested mode with a horizontal resolution
ranging from 100 m in the vicinity of the link to 900 m in the remote parts of Øresund, and
with a vertical resolution of 1 m. MIKE 3 was subsequently calibrated and validated based
upon the intensive field campaign periods.
Amongst the comprehensive data sets from the monitoring programme, which form a
unique basis for modelling, a three-month period was selected as ‘design period’ such
that it reflected the natural variability of Øresund. The design period was used in the
detailed planning and optimisation of the link, and to define the compensation dredging
volumes, which were required to reach a so-called zero-solution.
MIKE 21
2 Hydrodynamic Module - © DHI
1.2 Objective of Training Example
The objective of this training example is to set up a simplified MIKE 21 Flow Model for
Øresund from scratch and to calibrate the model to a satisfactory level.
The exercise has been made as realistic as possible, although some short cuts have
been made with respect to the data input. This mainly relates to quality assurance and
pre-processing of raw data to bring it into a format readily accepted by the MIKE Zero
software. Depending on the amount and quality of the data sets this can be a tedious,
time consuming but indispensable process. For this example the ‘raw’ data has been
provided as standard ASCII text files.
The files used in this Step-by-step training guide are a part of the installation. You can
install the examples from the MIKE Zero start page.
Please note that all future references made in this Step-by-step guide to files in the
examples are made relative to the main folders holding the examples.
User Guides and Manuals can be accessed via the MIKE Zero Documentation Index in
the start menu.
If you are already familiar with importing data into MIKE Zero format files, you do not have
to generate all the MIKE Zero input parameters yourself from the included raw data. All
the MIKE Zero input parameter files needed to run the example are included and the
simulation can start immediately if you want.
1.3 Tasks to be completed to form a Complete Hydrodynamic Setup
Bathymetry setup
• Set up of Bathymetry by importing geographical data with soundings based on a
survey or digitised from nautical chart
Creation of boundary conditions
• Set up water levels at the boundaries
• Set up of Wind condition
For the model verification of the hydrodynamic model we need simultaneous
measurements of water levels and current speed inside the model area.
Creation of verification data
• Create data set with current speed and direction
• Create data set with water levels
Creating the Bathymetry
3
2 Creating the Bathymetry
Figure 2.1 Chart covering the area of interest
MIKE 21
4 Hydrodynamic Module - © DHI
Based on the sea chart we define our working area in the Bathymetry Editor
Figure 2.2 Defining the Working Area
Define the Working Area (UTM Zone 33) with origin at Easting 290000 and Northing
6120000 and with a width of 120000 m and a height of 120000 m. (See Figure 2.2) The
resulting Working Area is show in Figure 2.4.
Import digitised shoreline data (land.xyz) and digitised water data (water.xyz) from ASCII
files (see example in Figure 2.5). Remember to convert from geographical co-ordinates
(WorkArea Background Management Import). See Figure 2.6.
Figure 2.3 ASCII file describing the depth at specified geographical locations (Longitude,
Latitude and Depth)
Creating the Bathymetry
5
Figure 2.4 Working Area
Figure 2.5 Background Management
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Figure 2.6 Import digitised Shoreline and Water Depth from ASCII files
Figure 2.7 Working Area after import of land and water data
Creating the Bathymetry
7
Next define the Bathymetry (WorkArea Grid Bathymetry Management New)
Figure 2.8 Grid Bathymetry Management
Specify the Bathymetry as follows:
• Grid spacing 900 m
• Origin in 337100 m East and 6122900 m North
• Orientation 327 degrees.
• Grid size 72 in x-direction and 94 in y-direction.
Figure 2.9 Defining the bathymetry
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Figure 2.10 Working Area with imported depth values and defined bathymetry (the black
rectangle)
The Working Area will now look like the one illustrated in Figure 2.10, where a bitmap
actually has been included as a background image (map.gif). The image can be used for
manual digitising or adjusting some areas using some of the tools on the menu bar.
Now import data from background (click on ‘Import from Background’ and drag mouse
over points of interest, selected points are now changing colour, finally click on ‘Import
from Background’ once more). Now we are ready for interpolation of the xyz data to grid
points (WorkArea Bathymetry Management Interpolate). Save the bathymetry
specification file and load the generated dfs2 file into the Grid Editor, for example.
Creating the Bathymetry
9
Figure 2.11 Grid Editor showing the interpolated bathymetry
Make some adjustment in order to obtain only two boundaries, namely the northern and
southern boundary. Close the eastern boundary by assigning land at the southern part of
the eastern boundary and fill up the small lakes around in the bathymetry and inspect the
land water boundary carefully. Furthermore, inspect the bathymetry close to the
boundaries avoiding areas with deeper water just inside the boundaries. Adjust the north
boundary so it is open from 60 to 69 along line 93. Adjust the south boundary so it is open
from 1 to 30 along line 0. Use land values to fill the areas close to the boundaries as
shown in Figure 2.11.
The Grid Plot control in Plot Composer can now be used to make a plot of the bathymetry.
Select File New Plot Composer. From the menu bar select Plot Insert New Plot
Object. Select Grid Plot. Right-click on the Plot Area, select properties and select the
Master file.
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Figure 2.12 Plot of the adjusted Bathymetry
Creating the Input Parameters
11
3 Creating the Input Parameters
3.1 Generate Water Level Boundary Conditions
Measured water level recordings from four stations located near the open model
boundaries force the Øresund model. Due to strong currents and because the influence of
the Coriolis effect is significant, water level recordings at each end of the open boundary
are required.
The objective of this example is based on measured recordings from four stations to
create two line series with water level variations. The locations of the four stations are
listed in Table 3.1.
Table 3.1 Measured water level data
Station
Data File
Position
Easting
(m)
Northing
(m)
WL1 WL1.txt 385929 6243197
WL2 WL2.txt 338957 6220549
WL3 WL3.txt 348310 6225949
WL4 WL4.txt 362880 6137713
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Figure 3.1 Map showing the individual stations (LH = Light House)
3.1.1 Importing measured water levels to time series file
Open the Time Series Editor. Select the ASCII template. Open the text file WL1.txt.
Change the time description to ‘Equidistant Calendar Axis’ and click OK. Then right-click
on the generated data and select properties change the type to ‘Water Level’. Save the
data in wl1.dfs0. Repeat these steps for the remaining 3 stations.
Creating the Input Parameters
13
Figure 3.2 ASCII file with water level recordings from Station 1
Figure 3.3 Time Series Editor Import template
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Figure 3.4 Time Series Properties
Figure 3.5 Time Series Editor with imported Water Levels from Station 1
Creating the Input Parameters
15
To make a plot of the water level time series, open the plot composer select ‘plot’
‘insert a new plot object’ and select ‘Time Series Plot’ (see Figure 3.6). Right-click on the
plot area and select properties. Then find the actual time series file and change some of
the properties for the plot, if any (see Figure 3.8).
Figure 3.6 Plot Composer inserted a new Plot Object as Time Series
If several time series files are to be plottet in the same plot, right-click on the plot area and
select new item (see Figure 3.7).
Figure 3.7 Plot Composer Time Series Plot Properties select new item
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Figure 3.8 Plot Composer properties select time series to plot
Figure 3.9 and Figure 3.10 show the measured water levels at the two boundaries.
Figure 3.9 Combined Time Series at the North Boundary Station 1 and 2
Figure 3.10 Combined Time Series at the North Boundary Station 3 and 4
Creating the Input Parameters
17
3.1.2 Creating boundary conditions
Now you must define the boundary in a shape that correlates to the bathymetry.
Determine the width of the two boundaries (use for instance Grid Editor). Load Profile
Series and select ‘Blank ...’. Fill in the required information:
North boundary
• Start date 1993-12-02 00:00:00
• Time step: 1800s
• No. of time steps: 577
• No. of grid points: 10 (60 – 69 line 93)
• Grid Step: 900m
Load Station 1 (WL1.dfs0) and copy and paste the water levels to the profile Series Editor
at point 0. Next load Station 2 (WL2.dfs0) and copy and paste the levels into point 9 (see
Figure 3.12). Then select tools and interpolate the profile series. Save the profile series as
WLN.dfs1 (see Figure 3.13).
Figure 3.11 Profile Series Properties
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Figure 3.12 Copying WL1 and WL2 into Profile Series Editor
Figure 3.13 Interpolated Water Level at the North boundary
Creating the Input Parameters
19
Repeat the same steps with the southern boundary with the similar information except the
number of grid points and using the recorded water levels at station 3 (WL3.dfs0) and 4
(WL4.dfs0) and save the resulting file as WLS.dfs1.
South boundary
• Start date 1993-12-02 00:00:00
• Time step: 1800s
• No. of time steps: 577
• No. of grid points: 30 (1 – 30 line 0)
• Grid Step: 900m
3.2 Initial Surface Level
The initial surface level is calculated as a mean level between the northern and the
southern boundary at the beginning of the simulation. Load the two boundary files and
approximate a mean level at the start of the simulation. We will use –0.38m.
3.3 Wind Conditions
Wind recordings from Kastrup Airport will form the wind condition as time series constant
in space. Load the time series editor and import the ASCII file ‘WindKastrup.txt’ as
equidistant calendar axis. Save the file in ‘WindKastrup.dfs0’. Time series of the wind
speed and direction is shown in Figure 3.14, Figure 3.15 and Figure 3.16.
A more descriptive presentation of the wind can be given as a wind speed diagram. Start
the ‘Plot composer’ insert a new plot object select ‘Wind/Current Rose Plot’ and then
select properties and select the newly created file ‘WindKastrup.dfs0’ and change
properties to your need. The result is shown in Figure 3.17.
Figure 3.14 ASCII file with Wind speed and direction from Kastrup Airport
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Figure 3.15 Measured wind direction at Kastrup Airport
Figure 3.16 Measured wind speed at Kastrup Airport
Figure 3.17 Wind Rose from Kastrup Airport
Creating the Input Parameters
21
3.4 Density Variation at the Boundary
As the area of interest is dominated with outflow of fresh water from the Baltic Sea and
high saline water intruding from the Ocean measurement of salinity and temperature has
taken place at the boundaries. Depth average values of these measurements are given
as ASCII files named: SalinityNorthBnd.txt, SalinitySouthBnd.txt, TemperaturNorthBnd.txt
and TemperaturSouthBnd.txt. Examples are shown in Figure 3.18. Import these ASCII
files with the time series editor and save the files with the same name but with extension
dfs0. Remember to change the time description to ‘equidistant calendar axis’.
A
B
Figure 3.18 ASCII files with average temperature at the North boundary (A) and average salinity
at the South boundary (B)
A plot of the measured data is shown in Figure 3.19 and Figure 3.20.
Figure 3.19 Measured average temperature at North and South boundary
MIKE 21
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Figure 3.20 Measured average salinity at the North and South boundary
Model Setup
23
4 Model Setup
4.1 Flow Model
We are now ready to set up the model using the above boundary conditions and forcing.
Initially we will use the default parameters and not take into account the effect of the
density variation at the boundaries. The setup consists of the following parameters:
Parameter Value
Module Hydrodynamics only
Bathymetry Bathy900
Simulation Period 1993-12-02 00:00 – 1993-12-14 00:00
Time step 300s
No. of Time steps 3456
Enable Flood and Dry Drying depth 0.2 Flooding depth 0.3
Initial surface level 0.38
North Boundary (60 – 69) along line 93
North Boundary Type 1 data: WLN.dfs1
South Boundary (1 – 30) along line 0
South Boundary Type 1 data: WLS.dfs1
Eddy Viscosity Smagorinsky formulation, velocity based. Constant 0.5
Resistance Manning number. Coefficient 32
Result file HD01.dfs2
In the following, screen dumps of the individual input pages are shown and a short
explanation is provided.
MIKE 21
24 Hydrodynamic Module - © DHI
Figure 4.1 Flow Model: Module Selection
Specify Hydrodynamics only
Figure 4.2 Flow Model: Bathymetry
Specify the bathymetry Bathy900.dfs2. The projection zone will be defined as UTM-33
automatically.
Model Setup
25
Figure 4.3 Flow Model: Simulation period
Specify a time step, which will result in a Courant between 1 and 7. Start with a time step
of 300s. The time step range must be specified to 3456 time steps in order to simulate a
total period of 12 days.
Figure 4.4 Flow Model: Boundary
Select Program detected boundary conditions. If you have more than two boundaries, you
must inspect you bathymetry again.
MIKE 21
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Figure 4.5 Flow Model: Source and Sink
If you have any sources or sinks these have to be specified. Here in our case we do not
have any.
Figure 4.6 Flow Model: Flood and Dry
Specify Flooding and Drying depth. In our case, select the default values.
Model Setup
27
Figure 4.7 Flow Model: Initial Surface Level
After inspection of the boundary condition at the simulation start time decide the initial
surface level, or if the variation is large decide for an initial surface level map. In this case
we will use a constant level of -0.38m, which is the average between our north and south
boundary at the start of the simulation.
Figure 4.8 Flow Model: Boundary
Specify the type of boundary as a type 1 profile time series and select wln.dfs1 at the
northern and wls.dfs1 at the southern boundary.
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Figure 4.9 Flow Model: Boundary Type
To select the boundary type, move the cursor to the type field and click on this then select
Type 1 Data file.
Figure 4.10 Flow Model: Boundary Select File
Model Setup
29
Next, locate the appropriate data file in the file box to the right.
Figure 4.11 Flow Model: Source and Sink
The discharge magnitude and velocity for each source and sink is given here. But, since
we do not have any sources, leave it blank.
Figure 4.12 Flow Model: Eddy Viscosity
Change the default Eddy viscosity to Smagorinsky formulation with a coefficient of 0.5.
MIKE 21
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Figure 4.13 Flow Model: Bed Resistance
We will start the default Bed Resistance with a value given as a Manning number at
m1/ 3
/s. Later on we will use this value for calibration purposes.
Figure 4.14 Flow Model: Wind Conditions
To use the generated wind time series, we specify ‘Constant in Space’ and locate the time
series WindKastrup.dfs0. Use the default value for the friction.
Model Setup
31
Figure 4.15 Flow Model: Result
Specify one output area and specify the resulting output file name. The actual output size
is calculated on beforehand. Make sure the required disk space is available on the hard
disk.
Figure 4.16 Flow Model: Result Output Area
Reduce the output size to a reasonably amount by selecting an output frequency of 1800s
which is a reasonably output frequency for a tidal simulation. As our time step is 300s
then the specified output frequency is 1800/300 = 6. Area-wise, select the full area.
MIKE 21
32 Hydrodynamic Module - © DHI
Figure 4.17 Flow Model: Result Output File Name
Specify the file name HD01.dfs2 for our first simulation.
Now we are ready to run the MIKE 21 Flow model.
After the simulation use the Plot Composer (or Grid Editor, Data Viewer) to inspect and
present the result. Two plots are shown below; one with current towards North (Figure
4.18) and one with current towards South (Figure 4.19).
Figure 4.18 Current Speed and Water Level during current towards North
Model Setup
33
Figure 4.19 Current Speed and Water Level during current towards South
4.2 Model Calibration
In order to calibrate the model we need some measurements inside the model domain.
Measurements of water level and current velocities are available.
4.2.1 Measured water levels
Measurements of water level are given at station Drogden (WaterLevelDrogden.txt) and
Ndr. Roese (WaterLevelNdrRoese.txt) import these ASCII files using the Time Series
Editor, cf. Figure 4.20 and Figure 4.21.
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Figure 4.20 Drogden: Measured Water Level
Figure 4.21 Ndr. Roese Measured Water Level
4.2.2 Measured current velocity
To calibrate the current velocity, measured current is given at station Ndr. Roese
(CurrentNdrRose.txt) Import this file with the Time series Editor. Plots of current velocity
and current speed and direction are shown in Figure 4.22, Figure 4.23 and Figure 4.24.
Furthermore, a Speed/Direction diagram of the measured current is shown in Figure 4.25.
Figure 4.22 Ndr. Roese Measured Current Velocity East and North Component
Model Setup
35
Figure 4.23 Ndr. Roese Measured Current Speed
Figure 4.24 Ndr. Roese Measured Current Direction
Figure 4.25 Ndr. Roese Current Rose
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36 Hydrodynamic Module - © DHI
4.2.3 Model extraction
Now we are ready to extract water level and current speed from the simulation at the
points corresponding to Ndr. Roese: Point (43,33) and Drogden Point (37,22). Start the
‘MikeZero Toolbox’ then click on the + sign in front of Extraction and select ‘Time Series
from 2D files’. Figure 4.28 to Figure 4.34 show the corresponding dialogue pages for
extracting the results.
Figure 4.26 Select MIKE Zero Toolbox
Figure 4.27 Select Time Series from 2D files
Model Setup
37
Figure 4.28 Name of the Time Series Extraction
Figure 4.29 Specify the Hydrodynamic Result file
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Figure 4.30 Specify the Extraction Period
Figure 4.31 Specify the items to extract
Model Setup
39
Figure 4.32 Specify the extraction points
Figure 4.33 Specify the Time Series Output file
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Figure 4.34 Click Execute to extract the selected data
4.2.4 Compare model results and measured values
Compare the extracted values with measured values. Use the Plot Composer to plot the
simulated and measured water level and current.
The comparison is shown in Figure 4.35 for water level at Drogden and for Water Level at
Ndr. Roese on Figure 4.36. Current comparison for Ndr. Roese is shown in Figure 4.37.
Figure 4.35 Water Level comparison at Drogden
Model Setup
41
Figure 4.36 Water Level comparison at Ndr. Roese
Figure 4.37 Comparison of Current Velocity North at Ndr. Roese. Simulated with a Manning
number of 32 m1/ 3
/s.
The comparison between measured and calculated water level shows a reasonable
agreement. But the current velocity shows that the calculated speed is too low. To adjust
this we make a new calibration with a new Manning number of 44 m1/3
/s to decrease
resistance to the flow. Load the former simulation specification HD01.M21 and change the
Manning number to 44 m1/ 3
/s. Change the output file name to HD02.dfs2. Save the
specification as HD02.M21 and run the simulation with the new specification.
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Figure 4.38 Status window for execution of HD model
Extract the new time series similar to the former one and make a new plot of the
comparison. The result is shown in Figure 4.39.
Figure 4.39 Comparison of Current Velocity North at Ndr. Roese with a Manning number of
44 m1/ 3
/s.
The calculated current speed is closer to the measured, but still we need a little more
calibration. Including the density variation at the boundary will also improve the
calibration. Try to make the calibration by increasing the Manning number and reducing
the Eddy coefficient. For each calibration only change a single parameter and track the
changes in a log.
A major improvement in the calibration process could be obtained by using variable wind
friction.